04 DST Concepts

DST CONCEPTS

Module Objectives

To describe the DST concepts

To identify the main DST tools and their functionalities

To go through a DST example

To review the different DST configurations

Definitions DST :Temporary completion of the well with downhole tools to control the WELL under dynamic reservoir

conditions

A reservoir test can only be performed under dynamic conditions. This means the reservoir must be exposed to a disturbance that will cause the reservoir pressure to change

This pressure change, when recorded and interpreted along with the measured flow rates, will yield information about the reservoir parameters and geometry

Pressure Disturbance

Creation of a pressure disturbance depends on whether the reservoir is producing or shut in:

if the well has been shut in for a long time, flowing the reservoir creates the disturbance. This is called drawdown

if the well has been flowing for a long time, shutting in the well creates the disturbance. This is called build up

Disturbance can also be created by increasing or decreasing the flow rate

Flowing the well at several flow rates

using different choke sizes while measuring the stabilized

bottomhole pressure and temperature with accurate downhole gauges for each corresponding choke

Pressure Disturbance Data

The primary DST functions, whether conducted in open hole or cased wells, are to: Isolate the target zone. Control well flow. Convey fluid to surface. Acquire downhole data.

DST Concepts

1. The string channels the flow to surface.

2. The packer is a rubber element to isolate the zone to be tested.

3. The valve provides a method of controlling the well near the reservoir.

4. circulating valve provides communication between annulus and tubing.

The 4 basic equipment for a DST consist of a string (tubing or drill pipe), a packer a tester and a circulating valve.

DST Key Components

Circulating valve

Pc

Pf

Ph

Drill pipe or Tubing

Tester Valve

Packer

Annulus pressure (Ph)

Cushion pressure (Pc)

Formation pressure (Pf)

Pc < Pf < Ph

Circulate/ Reverse Valve

TCP guns

Casing

Downhole Pressures

The Packer isolates the formation from the annulus, the two pressures (Ph and Pf) must be isolated from one another.

The Tester valve : - controls the formation. - shut the well downhole to minimize wellbore storage effect - isolates annular fluid from cushion while RIH, preventing U-tubing -provides a seal for pressure test the string

After the packer is set and sealed, the test valve can then be opened and hydrocarbons can be produced to surface. This will only occur if Pc < Pf

DST Tools 1/2

Jars

Gauge carrier

1. Open the reverse circulating valve and Reverse out (flush hydrocarbons from drill pipe or tubing).

2. Close the reverse circulating valve.

3. Open the tester valve.

4. Pump mud into test string to kill the tested interval.

5. Unseat the packer.

6. Pull the string out of the hole (POOH)

The circulating valve can be used for ending a DST :

DST Tools 2/2

During the initial phase of the test, the well bore fluids, and later, the drilling fluid (mud) that has invaded the formation in the vicinity of the well bore flow to surface. This is the cleanup. It is complete when the well effluent at surface is pure reservoir fluid.

Once cleanup is complete, the main flow period can be maintained for the planned duration, during which downhole pressure measurements and surface flow rates are recorded. At the end of the main flow period, the tester valve is closed. Formation pressure builds up against the valve while downhole pressure measurement continues.

DST Operation Summary

BHP

Time

Pressure & Temp Recorders

RIH and Set Packer

Example of a DST Sequence 1/9

BHP

Time

Open Tester valve


BHP

Time

Flow well


BHP

Time

Shut in well


Circulating Valve

BHP

Time

Open circulating valve


BHP

Time

Reverse Out String Content


kill the tested interval BHP

Time Circulating Valve closed first

Apply pressure in to annulus to open Tester valve

Tester Valve is open

Open tester valve and bullhead


BHP

Time

Unset Packer


BHP

Time

POOH


Types of DST

Well Location & Configuration

PACKERS are designed to isolate the perforated interval from the mud column. The weight applied on the packer compress its rubber elements against the casing and creates a seal between the annulus and tubing.

Three main types of Packers

- FlexPac packer

- PosiTest packer

- Positrieve packer

DST Packers

FlexPac PosiTest Positrieve

DST Types of Packers

-2 Parts

-Upper & lower slips

-DP 7500 psi

-WP 10 kpsi

-1 Part

-Only lower slips

-Is not used for stimulation jobs

-1 integral Part

-Upper and lower slips

-DP 12kpsi

-WP 15 kpsi

Various types are available:

- MFE (Multi Flow Evaluator)

Operated by manipulation of the test string.

Applications: Only fixed rigs (onshore & jack-up)

- PCT (Pressure Controlled Tester)

Operated by annulus (and tubing) pressure.

Application: Offshore, floating facilities, only cased hole.

- IRIS dual-valve tool (IRDV)

(IRIS= Intelligent Remote Implementation System)

Operation & application similar to PCT

DST Tester Valves

IRDV valve PCT valve

IRDV & PCT Valves

- 1 tester valve

- 1 circulating valve

- 1 electronic module

- lower operating pressures than PCT

- pre-programmed sequences

- 1 tester valve

- 1 hold open module

-1 Nitrogen chamber

- longer than IRDV

Tubing or drillpipe

Slip joints (2 or more)

Drill collars

Redundant circulating valve

Drill collars

Circulating valve

RA marker

Drills collar

Surface readout

Downhole tester valve

Hydrostatic reference tool

Pressure recorders (2 or more)

Hydraulic jar

Safety joint

Packer

Slotted tailpipe

Debris sub

Tubing

Firing head

Safety spacer

Perforating gun

DST/TCP String

Example of a DST / TCP string

THE END

DST CONCEPTSSlide Number 2Module Objectives Definitions Pressure Disturbance Slide Number 6Slide Number 7Slide Number 8Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 19Slide Number 20Slide Number 21Slide Number 22Slide Number 23Slide Number 24Slide Number 25Slide Number 26Slide Number 27Slide Number 28Slide Number 29

04 DST Concepts

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